List of fallacies

A fallacy is an error in reasoning that undermines an argument's support for its conclusion. In academic usage, the term usually applies to arguments, although it is sometimes used more broadly for errors in reasoning in explanations, definitions, questions, or other forms of discourse. A fallacious argument may nevertheless have a true conclusion; the defect lies in the inadequate reasoning offered in support of it.

Fallacies are commonly divided into formal and informal fallacies. A formal fallacy is a defect in an argument's logical form that makes a deductive argument invalid. Informal fallacies cannot ordinarily be identified from form alone, since their assessment depends on such factors as content, evidence, context, and the purpose of the argument. They are often grouped under headings such as relevance, ambiguity, presumption, faulty generalization, and faulty causal reasoning, although the classification and boundaries of individual fallacies vary among authors.

Fallacies may be used deliberately to persuade, but they can also arise unintentionally through cognitive bias, ambiguity, or faulty inference. In deductive reasoning, a formal fallacy renders an argument invalid. In non-deductive reasoning, fallacious reasoning may make an argument weak, irrelevant, insufficiently supported, or otherwise inadequate without making its conclusion false.